I'm not sure that Ruby properly handles exclusive File access on Windows, based on what I see in the Ruby code here:

The 3rd parameter is `dwShareMode` which according to [MSDN docs](http://msdn.microsoft.com/en-us/library/windows/desktop/aa363858\(v=vs.85\).aspx#dwShareMode) should be set to `0` when asking for exclusive access, and while `EXCL` does pop up in here, I'm not sure I see the correlation with how that value gets set.  Of course, it's possible I've also completely missed it.
https://github.com/ruby/ruby/blob/21f81885ab310f564fb60bfe7dcde816eeb11994/win32/win32.c#L5697

I've run across a bunch of other instances where the Ruby file code behavior varies between Windows and other platforms, so it's at least worth taking a closer look at it.

Note that we did add the FFI definition for `CreateFile` as part of the symlink support, so we do have access to it we're looking to create the appropriate Windows variation.
https://github.com/puppetlabs/puppet/blob/e327840b104e6ad66696d8e82eb272b07da75476/lib/puppet/util/windows/file.rb#L121